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Indian Pediatr 2015;52: 19-20 |
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Does Healthy Diet Matter in Asthma Prevention
and Control?
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*#Jun Ma and
#Nan Lv
From *Palo Alto Medical Foundation Research
Institute, Palo Alto; and #Department of Medicine,
Stanford University School of Medicine, Stanford; CA, USA.
Email: [email protected]
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Asthma is a global public health problem with
substantial burden, particularly in terms of disability and limited
quality of life. Asthma affects millions of people of all ages
worldwide, with some data showing increased prevalence in recent years,
especially among children in low- and middle-income countries [1]. Among
a multitude of possible contributing factors, changes in diet
composition and worsening nutritional quality have been implicated in
the epidemiology of asthma [2]. Previous studies have suggested that
some individual nutrients (e.g., long-chain polyunsaturated fatty acids,
vitamin D, and antioxidants) or individual food groups (e.g.,
fruits, vegetables, and fish) may be associated with the etiology and
biophysiology of asthma [3-6]. Because diet is a complex combination of
foods from various groups and human nutritional status is dependent on
the interplay of the nutrients that are naturally present in the
whole-food admixture, there is an increasing interest in examining the
impact of overall dietary patterns on asthma development and progression
[7].
The study by Halpern-Silveira and colleagues [8] in
this issue of Indian Pediatrics focused on this important
emerging topic. This cross-sectional case-control study was designed to
investigate the association of specific foods, food groups and a
Mediterranean diet with asthma severity in 268 children with persistent
asthma and 126 age-matched controls with intermittent asthma. The
children were 3 to 12 years old and recruited from 2 teaching hospitals
in Brazil. Performed by pulmonologists specialized in childhood asthma,
diagnosis of asthma was based on the 2009 British Thoracic Society
Guidelines, and severity classifications included intermittent and
persistent asthma (mild, moderate, or severe) according to the 2007 US
Guidelines for the Diagnosis and Management of Asthma. The consumption
frequency of specific foods or food groups in the past 12 months among
these children was classified as frequent ( ³3
times/week) or infrequent (<3 times/week) as per interviews with their
parents or guardians using a standard pre-coded questionnaire. Two
dietary patterns were defined based on consumption of at least five
foods in each group, 3 times or more per week: a pro-Mediterranean diet
(fruit, vegetables, fish, fruit juices, root vegetables and tubers and
grains) and a contra-Mediterranean diet (milk, meat, eggs, processed
foods, soft drinks, butter). The results showed no significant
association of asthma severity either with the consumption frequency of
the specific foods and food groups, or with pro- or contra-Mediterranean
diet.
Several recent reviews have suggested potential
beneficial effects of certain nutrients, foods, and dietary patterns on
asthma. A systematic review and meta-analysis by Nurmatov, et al.
[5] assessed the relationship between childhood and maternal diets and
asthma in children aged £16
years. The authors concluded that while the available epidemiologic
evidence was weak, vitamins A, D and E, fruits and vegetables, and
Mediterranean diet appeared to be protective for the prevention of
asthma in children. Two other systematic reviews and meta-analyses
specifically evaluated the relationship between dietary patterns and
asthma [7,9]. Garcia-Marcos, et al. [9] investigated the
association of Mediterranean diet with ever asthma, current wheeze and
current severe wheeze, and if present, whether the relationship was
specific to the Mediterranean regions. Their meta-analysis showed that
adherence to Mediterranean diet was negatively associated with current
wheeze and current severe wheeze in Mediterranean regions, but with ever
asthma in non-Mediterranean regions; it was unclear why geographic
regions had such a modifying effect. When considering all regions
together, adherence to Mediterranean diet appeared to be protective
against current wheeze and ever asthma, but not against current severe
wheeze. Our group recently published a systematic review of studies
investigating the impacts of dietary patterns on asthma in adults,
children, and pregnant women-child pairs [7]. We included six additional
studies in children that were not in the review by Garcia-Marcos and
company. Five of these studies [10-14] reported either a beneficial
effect of Mediterranean diet or a detrimental effect of an unhealthy
dietary pattern (e.g., Western pattern) on asthma outcomes, such
as prevalence, symptoms and lung function, in children. Thus, these
studies lend support to the conclusion that Mediterranean diet may be
beneficial for children with asthma.
The generally consistent finding of possible
beneficial effects of Mediterranean diet on both the prevention and
management of asthma in pediatric populations is encouraging, but there
are also important caveats. The studies included in these reviews used
differing methods to define and measure Mediterranean diet (e.g.,
categorical vs. continuous Mediterranean diet variables generated
from dietary instruments of varying reliability and validity), and
assessed heterogeneous asthma outcomes (e.g., prevalence of ever
or current asthma or wheeze, asthma symptoms, and lung function), which
made it challenging to draw a unanimous conclusion. Furthermore, the
quality of the evidence is weak overall because most studies to date
were cross-sectional, precluding investigation of temporal or causal
relationship between diet and asthma. Because of the lack of
experimental studies, it remains unclear whether healthy eating can
indeed prevent and/or treat asthma. On the basis of encouraging
epidemiologic data, well-designed and well-conducted randomized
controlled trials are needed to examine the efficacy of Mediterranean
diet for asthma prevention and control, and to elucidate the underlying
mechanisms.
Funding: This research was supported by grant R34
HL108753 from the National Heart, Lung and Blood Institute and internal
funding from the Palo Alto Medical Foundation Research Institute. The
content is solely the responsibility of the authors and does not
necessarily represent the official views of the National Heart, Lung,
and Blood Institute. No sponsor or funding source had a role in the
preparation, review, or approval of the commentary.
Competing interest: None stated.
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